The invention relates to a valve arrangement with a first and a second fluid connection, a valve member which is biased into a first position by a spring arrangement, in which the first and the second fluid connections are blocked from each other, and an actuation means adapted to move the valve element into a second position in which the first and the second fluid connections are in a primary flow connection.
Such a valve arrangement is known among others as a so-called "normally closed" valve. As is already indicated by this term, the flow connection between the fluid connections is blocked in the non-actuated condition, i.e. in the basic or normal, respectively, condition, while the flow connection between the fluid connections is made in the actuated condition. In order to block the flow connection between the fluid connections in the non-actuated condition, a valve element is biased under the action of a spring arrangement, so that it sealingly contacts a sealing seat. In order to make the flow connection between the fluid connections in the actuated condition, it is necessary that the actuation means exerts a force which is capable of at least overcoming the biasing force of the spring arrangement, so that the valve element is lifted off the sealing seat.
However, it is not sufficient for most applications if the actuation means exerts a force which is only minimally higher than the biasing force of the spring arrangement, because during operation different fluid pressures occur at the fluid connections of the valve arrangement so that, in addition, a pressure differential force acts on the valve member, which, depending on the effective direction, counteracts the force applied by the actuation means. Accordingly, the actuation means is to be designed in such a manner that the actuation force is higher than the sum of the biasing force of the spring arrangement and the maximum pressure differential force to be expected in order to ensure a reliable function of the valve arrangement. The great disadvantage is that the actuation means is virtually over-dimensioned, in particular, if a large flow cross-section in the actuated condition of the valve arrangement is required, as is the case in the majority of the applications, in order to preclude a throttle effect of the valve arrangement. A large flow cross-section, however, additionally involves a very high pressure differential force so that consequently a high actuation force is to be applied. This causes high costs and great efforts in the design of the valve arrangement. In addition, the valve arrangement requires a relatively large installation space.
In view of the above, the object of the invention is to develop a valve arrangement which avoids the above mentioned drawbacks.